Vascular architecture generates fine scale variation in systemic induction of proteinase inhibitors in tomato

Systemic induction following damage has been found in many plant species. Despite this widespread appreciation for the importance of induction, few studies have characterized the spatial variability of induction. We used tomato, Lycopersicon esculentum, to examine how damage to a single leaf affected the spatial distribution of systemic induction of proteinase inhibition in leaves above the damaged leaf. We crushed each leaflet of the second true leaf with forceps and measured the spatial distribution of proteinase inhibition in leaves 3, 4, and 5 at 8, 16, 24, 48, 72, and 120 hr. Constitutive levels of proteinase inhibitor activity were quantified in undamaged plants. We hypothesized that, due to vascular control of signal movement, systemic induction would show both among and within leaf variability. Following damage to leaf 2, induction was most pronounced in leaf 5 and minimal in leaf 3. In general, proteinase inhibitor activity was greatest at 24 hr and then declined. As predicted by vascular architecture, the near side of leaves in adjacent orthostichies showed higher induction than the far side of leaves. There was no increase in proteinase inhibitor activity in the undamaged neighboring plants. Overall our results demonstrate that systemic induction of proteinase inhibitors is partially controlled by vascular architecture and that future studies on systemic induction should examine the vascular architecture of the plants being studied. We argue that this spatial variation may influence the performance of herbivores sensitive to induced chemical changes.